This invention relates to the preparation of metallosilazane polymers. More specifically this invention relates to the preparation of metallosilazane polymers which contain significant amounts of boron, phosphorous, or titanium. These polymers are useful as chemical intermediates to synthesize organosilicon compounds. These polymers are also useful, when fired at high temperatures, to form ceramic materials.
What is disclosed herein is a novel process to obtain novel metallosilazane polymers which consists of contacting and reacting chlorine-containing disilanes with disilazanes and metal halides in an inert, essentially anhydrous atmosphere and removing volatile byproducts.
Gaul in U.S. Pat. No. 4,340,619 (issued July 20, 1982) disclosed a method for preparing R.sub.3 'SiNH-containing silazane polymers by contacting and reacting, in an inert, essentially anhydrous atmosphere, chlorine-containing disilanes with (R.sub.3 'Si).sub.2 NH disilazanes where R' was a vinyl, hydrogen, alkyl of 1-3 carbon atoms, or phenyl group. The silazane polymers of Gaul were convertable to ceramic materials upon firing at elevated temperatures.
Yajima et al. in U.S. Pat. No. 4,220,600 (issued Sept. 2, 1980) disclosed a method for preparing a polycarbosilane by reacting a polyborosiloxane with a polysilane. The polyborosiloxanes were prepared by reacting boric acid (or its ester) with a diorganodichlorosilane or by reacting boric acid with diorganodialkoxylsilane. The preparation of borosiloxane polymers from boric acid and phenylsilane is described by Yajima et al. in U.S. Pat. No. 4,152,509 (issued May 1, 1979). The required polysilanes were prepared by dechlorinating a dichlorosilane with sodium metal. Therefore the method of Yajima required at least three reaction steps to prepare a polycarbosilane. The polycarbosilane contained significant amounts of oxygen in the polymer chain in the form of siloxane or B-O bonds. The polycarbosilane formed a ceramic material upon firing at high temperature. The ceramic yield was higher for the boron-containing polycarbosilane relative to a similar polycarbosilane without boron.
In U.S. Pat. No. 4,359,559 (issued Nov. 16, 1982), Yajima et al. repeated the preparation of a polymetallocarbosilane by reacting a polycarbosilane containing ##STR1## units with organometallic compounds MW.sub.4 where M was either titanium or zirconium and W was an alkoxy group, a phenoxy group, or an acetylacetoxy group. The polymetallocarbosilane produced by this method contains significant amounts of oxygen in the polymer chain in the form of siloxane or M-O bonds. A ceramic material was formed upon firing the polymetallocarbosilane at elevated temperatures.
In U.S. Pat. No. 4,347,347 (issued Aug. 31, 1982), Yajima et al. disclosed an organometallic copolymer containing a polycarbosilane portion and a polymetallosiloxane portion which were crosslinked. This copolymer was prepared by reacting a polycarbosilane with a polymetallosiloxane which contained units of formula --M--O-- where M is either titanium or zirconium and siloxane units of formula --Si--O--. This process consists of at least three steps since neither the polycarbosilane or polymetallosiloxane are readily available. The copolymer produced contains significant amounts of oxygen in the polymer chain in the form of siloxane units and --M--O-- units. Upon firing at elevated temperatures the copolymer is converted to a ceramic material.
What has been newly discovered is that certain metallosilazane polymers can be prepared by reacting disilanes with silazanes and reactive metal halides.